Members of the walking catfish family Clariidae originated in Asia around 50 million years ago, says a new study.

Agnese and Teugels of the University of Montpellier studied the evolutionary relationships of clariid catfishes, which occur in Asia and Africa, by undertaking a molecular analysis of 563 nucleotides of the cytochrome b mitochondrial gene.

The material analysed included 32 different clariid catfish species across seven different genera, as well as relatives including Clarotes laticeps (a member of the family Claroteidae) and the Stinging catfish Heteropneustes fossilis (a member of the Heteropneustidae).

Their paper, which is due to be published in the journal Molecular Phylogenetics and Evolution, shows that two distinct lineages are present among the fish examined and were made up of the African fishes on one side and the Asian species on the other.

Agnese and Teugels then used a molecular clock technique and analysis of similar species in the fossil record to estimate the time at which the fishes diverged.

They believe that, based on a 1% divergence every million years, the Asian clariid catfishes originated in Asian 50 million years ago, while the African ones originated from a common ancestor about 15 million years ago.

Interestingly, at different times during the evolutionary history of the family, some traits have evolved independently at different times.

Said Agnese and Teugels: \"Adaptation to life in deep water occurred two times independently in lake Tanganyika (with Dinotopterus cunningtoni) and in Lake Malawi (with Bathyclarias species). \"